An antenna is an element used for radiating or receiving electromagnetic waves. While antennas are available in numerous different shapes and sizes, they all operate according to the same basic principles of electromagnetics. According to Faraday's law, the induced electromotive force or emf in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit. Electromotive force, emf, measured in volts, refers to the energy gained per unit charge passing through a generating device. As used herein, the magnetic flux refers to the quantity of magnetism, or the strength of a given magnetic field, given by the equation:
  ℰ  =      -                            ⅆ                      Φ            B                                    ⅆ          t                    .      where
∈ is the electromotive force (EMF) in volts
ΦB is the magnetic flux through the circuit (in webers).
The direction of the electromotive force (the negative sign in the above formula) is given by Lenz's law.
As a general principle, a guided wave traveling along a transmission line in an antenna will radiate free-space waves also known as electromagnetic waves. Conversely, when an antenna is receiving, it transforms free-space waves by inducing a guided electromagnetic wave within a transmission line. The guided electromagnetic waves are fed into a circuit, which converts them into a useful format.
When an antenna is transmitting, it receives the guided electromagnetic wave for transmission from a feed line and induces an electric field surrounding the antenna to form a free-space propagating electromagnetic wave. The features of an antenna can be described by parameters of operation such as frequency, radiation patterns, reflected loss, and gain.
An antenna may be a component of a device such as, for example, a cellular telephone, radio, television, or RADAR system that directs incoming and outgoing radio waves between free space and a transmission line. Antennas may be composed of metal or polymers filled with metal or carbonaceous particles and have a wide variety of configurations, from the whip or mast-like devices employed for radio and television broadcasting to the large parabolic reflectors used to receive satellite signals and the radio waves generated by distant astronomical objects.
Many types of portable electronic devices, such as cellular phones, GPS receivers, palm electronic devices, pagers, laptop computers, and telematics units in vehicles, need an effective and efficient antenna for communicating wirelessly with other fixed or mobile communication units, including satellites. Advances in digital and radio electronics have resulted in the production of a new class of personal communications equipment posing special problems for antenna designers.
Personal wireless communication devices have created an increased demand for compact antennas. The increase in satellite communication has also increased the demand for antennas that are compact and provide reliable transmission. In addition, the expansion of wireless local area has also necessitated the demand for antennas that are compact and inexpensive.
Wire antennas, such as whips and helical antennas, are sensitive to only one polarization direction. As a result, they are not optimal for use in portable communication devices which require robust communications even if the device is oriented such that the antenna is not aligned with a dominant polarization mode.
A patch antenna is a type of antenna that offers a low profile and easy manufacturability, great advantages over traditional antennas. Patch antennas are planar antennas used in wireless links and other microwave applications. Generally, conventional patch antennas use “patches” formed on the top surface of a thin dielectric substrate separating them from a conductive layer on the bottom surface of the substrate that constitutes a ground for the transmission line or antenna.
Reflector or dish antennas are commonly used in residential environments for receiving broadcast services, such as television channel signals from geostationary, or equatorial, satellites. Reflector antennas, however, are bulky and relatively expensive for residential use. Furthermore, inherent in reflector antennas are feed spillover and aperture blockage by a feed assembly, which significantly reduces their aperture efficiency. An alternative antenna, such as a patch antenna, overcomes many of the disadvantages associated with reflector antennas.
Patch antennas require less space, are simpler and less expensive to manufacture, and are more compatible than reflector antennas. A parabolic reflector antenna has a curved surface. A patch antenna can be made having a planar surface. Further, a patch antenna can achieve the concentration of an antenna beam in a particular direction by means of the application of one of several methods.
Patch antennas are particularly suitable for use as active antennas. An active antenna is an antenna having all of the necessary components, such as an antenna element, feeding circuits, active devices or active circuits, integrally provided on a monolithic substrate, thus producing compact, low cost, and multi-function antenna equipment.
Additionally, the planar structure of a patch antenna permits it to be conformed to a variety of surfaces having different shapes. Patch antennas can be designed to produce a wide variety of patterns and polarizations, depending on the mode excited and the particular shape of the radiating element used. This results in the patch antenna being applicable to many military and commercial devices, such as, for example, use on aircraft or space antennas.
There is an increasing demand for the use of patch antennas in wireless communication due to their inherently low back radiation, ease of conformity and high gain as compared to wire antennas. The patch antenna design prevents large amounts of radiation from being produced at the back of the antenna.
Patch antennas comprise one or more conductive rectilinear or ellipsoidal patches supported relative to a ground plane and radiate in a direction substantially perpendicular to the ground plane. As opposed to a conventional wire-based antenna, generally the conventional patch antenna comprises a plurality of generally planar layers including a radiating element, an intermediate dielectric layer, and a ground plane layer. The radiating element is an electrically conductive material imbedded or photo etched on the intermediate layer and is generally exposed to free space.
Depending on the characteristics of the transmitted electromagnetic energy desired, the radiating element may be square, rectangular, triangular, or circular and is separated from the ground plane layer. An exemplary conventional patch antenna may include a transmission line feed, multiple dielectrics, and a metalized patch on one of the dielectrics. In a typical conventional patch antenna, the radiator element is provided by a metallic patch that is fabricated onto a dielectric substrate over a ground plane.
The conventional dual-band signal-layer patch antenna has been widely used in applications like radar and communication systems because of its advantages over a conventional antenna, such as lighter weight, lower profile and lower cost. Generally, dual-band single-layer patch antennas can be categorized into categories which include stub-type patch antennas, notch-type patch antennas, pin-and-capacitor-type patch antennas, and slot-loaded-type patch antennas.
The patch antenna has a very low profile and can be fabricated using photolithographic techniques. It is easily fabricated into linear or planar arrays and readily integrated with microwave integrated circuits. Patch antennas are commonly produced in half wavelength sizes, in which there are two primary radiating edges parallel to one another.
The performance of an antenna is determined by several parameters, one of which is efficiency. For a patch antenna, “efficiency,” as used herein, is defined as the power radiated divided by the power received by the input to the antenna. A one-hundred percent efficient antenna has zero power loss between the received power input and the radiated power output. Factors that determine patch antenna efficiency include the loss in the dielectric material, the surface wave loss, and conduction losses. Traditional patch antennas, designed with a dielectric material, have about 80% efficiency. For example, if the patch array antenna, designed on the dielectric, is excited with an input power of 1 kilowatt (KW), the antenna will radiate 800 watts (W) while 200 W are lost.
Patch array antennas typically rely on traveling waves and require a complex feed network which contributes significant feed loss to the overall antenna loss. Furthermore, many patch antennas are limited to transmitting and/or receiving only a linearly polarized beam. The substrate is mounted on a larger ground plane, which serves as the return path for current induced on the patch element.
A patch antenna operates by resonating at a frequency. The patch antenna performs optimally when it is sized such that the cavity beneath the patch resonates in its fundamental mode at the frequency of interest.
Microstrip antennas and patch array antennas have been developed over many decades because of their low profile structures. These antennas are often designed on dielectric materials and can have reduced efficiency owing to dielectric losses
As stated in the foregoing, in view of the deficiencies of the prior art, there exists a need for a more efficient, low-cost, high power antenna system operable at high frequencies.
The publication entitled “Functional Test Results of a High Power Patch Array Antenna,” Ly, Canh; January 2008; Report No.(s): AD-A475036; ARL-TR-4352; Defense Technical Information Center (DTIC), discloses mechanical and electrical test results of a high power two-patch array antenna. The mechanical test was run for 55 minutes for each axis of the antenna. The electrical test was conducted using a high power RF source (>1 KW) with single and two-patch array antennas. Although the first mechanical test results indicated that the screws of the antenna cover are loosened about ¼ turn, and right angle connectors inside the antenna enclosure box were loosened about a fraction of a turn, the antenna still sustained all functional operations. The antenna uses air dielectric to endure a high average power for the system that operates at S-Band in order to neutralize unattended microwave devices.